Circuit That Deciphers Between AC and DC Input Signals

ABSTRACT

Electronic devices require correct power in order to operate correctly. Receiving an incorrect power signal could potentially result in immediate and/or long term harm to the electronic device and/or catastrophic conditions. Certain devices, such as programmable logic controller (“PLC”) modules, may provide variable power to electronic devices, such as field devices comprising sensors and/or actuators. The present inventors have recognized that deciphering between AC and DC input signals before coupling electronic devices to such power sources may advantageously avoid harmful and/or catastrophic conditions. Aspects of the present invention provide an electronic circuit for deciphering between an AC and a DC input signal. Systems and methods are also described.

BACKGROUND OF THE INVENTION

The present invention relates to electronic circuits, and in particular,to an electronic circuit that deciphers between AC and DC input signals.

Electronic devices typically use power from alternating current (“AC”)and/or direct current (“DC”) sources. For example, an electronic devicemay receive an AC power signal from an AC power source for its power, ormay receive an AC power signal from an AC power source for internallyderiving a DC power signal for its power, or may receive a DC powersignal from a DC power source for its power. Some electronic devicescould use both AC power signals and DC power signals concurrently forits power. In many industrial applications, AC power signals may beprovided by AC power sources between 87 to 265 Volts at 50 to 60 Hertz,and DC power signals may be provided by DC power sources between 18 to32 Volts.

Industrial controllers, such as programmable logic controllers(“PLC's”), are specialized electronic computer systems used for thecontrol of industrial processes or machinery, such as in a factoryenvironment. Industrial controllers differ from conventional computersin a number of ways. Physically, they are constructed to besubstantially more robust against shock and damage and to better resistexternal contaminants and extreme environmental conditions. Theprocessors and operating systems are optimized for real-time control andexecute languages allowing ready customization of programs to comportwith a variety of different controller applications. Industrialcontrollers may also have a user interface for accessing, controllingand/or monitoring the industrial controller, such as through a locallyconnected terminal having a keyboard, mouse and display.

Industrial controllers often have a modular architecture that allowsdifferent numbers and types of network cards or adapters to be used toconnect the controllers to electronic devices or field devices, such assensors and, actuators for controlling and interacting with industrialprocesses and/or machines. Field devices may be dedicated to aparticular function, such as detecting an input signals or running amotor, and may be located at convenient control points near theindustrial processes and/or machines. Field devices may receive ACand/or DC power locally, or in preferred applications, may receive ACand/or DC power from the industrial controller.

Electronic devices or field devices require correct power in order tooperate correctly. Receiving an incorrect power signal could potentiallyresult in immediate and/or long term harm to the electronic deviceand/or catastrophic conditions, including possible fire, personal injuryor death.

SUMMARY OF THE INVENTION

The present inventors have recognized that deciphering between AC and DCinput signals before coupling electronic devices, such as field devices,to a power source may advantageously avoid harmful and/or catastrophicconditions. As such, the present inventors have invented circuits,applications and methods for deciphering between AC and DC input signalsbefore coupling electronic devices to a power source.

Aspects of the present invention provide an electronic circuit fordeciphering between an AC and a DC input signal comprising: an AC filterreceiving an input signal and coupled to a first leg, the AC filterpermitting an AC signal to pass to the first leg and preventing a DCsignal from passing to the first leg; and a DC alter receiving the inputsignal and coupled to a second leg, the DC filter permitting a DC signalto pass to the second leg and preventing at least part of an AC signalfrom passing to the second leg. A DC signal passing to the second legcauses the second leg to produce a second output for indicating a DCinput signal, and an AC signal passing to the first leg causes the firstleg to produce a first output for indicating an AC input signal andcauses a lock out circuit to prevent the second leg from producing thesecond output.

The AC filter may comprise a series capacitor, and the DC filter maycomprise a series diode.

The first and second outputs may be coupled together to produce a thirdoutput for indicating an AC or a DC input signal. The first and secondoutputs may be coupled to light emitting diodes, and/or may produceaudible tones and/or digital data signals.

The lock out circuit may comprise a transistor in the second legcontrolled by circuitry in the first leg.

Another embodiment may provide a programmable logic controller modulefor providing power to a field device comprising: an enclosure; anelectrical terminal on the enclosure coupled to a power signal; an ACfilter contained in the enclosure receiving the power signal and coupledto a first leg of a circuit, the AC filter permitting an AC signal topass to the first leg and preventing a DC signal from passing to thefirst leg; and a DC filter contained in the enclosure receiving thepower signal and coupled to a second leg of the circuit, the DC filterpermitting a DC signal to pass to the second leg and preventing at leastpart of an AC signal from passing to the second leg. A DC signal passingto the second leg causes the second leg to produce a second output forindicating a DC power signal, and an AC signal passing to the first legcauses the first leg to produce a first output for indicating an ACpower signal and causes a lock out circuit to prevent the second legfrom producing the second output.

Yet another embodiment may provide a method for deciphering between anAC and a DC input signal comprising: (a) receiving an input signal; (b)permitting an AC component of the input signal to pass to a first leg ofa circuit while preventing a DC component of the input signal frompassing to the first leg; (c) permitting a DC component of the inputsignal to pass to a second leg of the circuit while preventing at leastpart of an AC component of the signal from passing to the second leg;and (d) producing a second output for indicating a DC input signalfollowing a DC component of the input signal passing to the second leg,and producing a first output for indicating an AC input signal andpreventing the second leg from producing the second output following anAC component of the input signal passing to the first leg.

These and other objects, advantages and aspects of the invention willbecome apparent from the following description. The particular objectsand advantages described herein may apply to only some embodimentsfalling within the claims and thus do not define the scope of theinvention. In the description, reference is made to the accompanyingdrawings which form a part hereof, and in which there is shown apreferred embodiment of the invention. Such embodiment does notnecessarily represent the full scope of the invention and reference ismade, therefore, to the claims herein for interpreting the scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a bank of programmable logic controller(“PLC”) modules for an industrial control system in accordance with anembodiment of the present invention;

FIG. 2 is an isometric view of an I/O module in accordance with theembodiment of FIG. 1;

FIG. 3 is an electronic circuit that deciphers between AC and DC inputsignals in accordance with an embodiment of the present invention;

FIG. 4 is another embodiment of an electronic circuit that deciphersbetween AC and DC input signals;

FIG. 5 is a diagram showing an industrial controller module and a fielddevice, each in accordance with an embodiment of the present invention;

FIG. 6 is an isometric view of a handheld diagnostic probe in accordancewith an embodiment of the present invention; and

FIG. 7 is a flow diagram illustrating a method for deciphering betweenan AC and a DC input signal in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

One or more specific embodiments of the present invention will bedescribed below. It is specifically intended that the present inventionnot be limited to the embodiments and illustrations contained herein,but include modified forms of those embodiments including portions ofthe embodiments and combinations of elements of different embodiments ascome within the scope of the following claims. It should be appreciatedthat in the development of any such actual implementation, as in anyengineering or design project, numerous implementation-specificdecisions must be made to achieve the developers' specific goals, suchas compliance, with system-related and business related constraints,which may vary from one implementation to another. Moreover, it shouldbe appreciated that such a development effort might be complex and timeconsuming, but would nevertheless be a routine undertaking of design,fabrication, and manufacture for those of ordinary skill having thebenefit of this disclosure. Nothing in this application is consideredcritical or essential to the present invention unless explicitlyindicated as being “critical” or “essential.”

Referring now to the drawings wherein like reference numbers correspondto similar components throughout the several views and, specifically,referring to FIG. 1, the present invention shall be described in thecontext of a bank of programmable logic controller (“PLC”) modules 10for an industrial control system in accordance with an embodiment of thepresent invention. The modules 10 include a series of enclosuresarranged from left to right, side by side, with complex shapes that maybe generally cubic. The series of enclosures may include a left mostmodule 12, followed by a first double, vertical terminal I/O module 14,followed by a second double, vertical terminal I/O module 16 andfollowed by a right most single, vertical terminal I/O module 18. Eachmodule, may be held in close proximity to the other by attachment to aDIN rail (not shown) thereby facilitating electrical connections side byside. The electrical connections side by side may provide a commonsystem backplane to form a network ring topology and may pass a modulepower signal starting from the left most module 12 to each neighboringmodule. Each module may also include one or more internal bus slots forreleasably receiving a function card and/or equivalently embedded logic.

An alternative embodiment may instead provide a single PLC module, abank of modules with greater separation and having electricalconnections supported by cabling, or any other electronic-based systemthat provides power for another device.

The left most module 12 may comprise a plurality of connectors 22, andvisual displays and/or LED's 20 for system monitoring, located on one ormore respective surfaces. The connectors 22 may include connections fornetworking, such as a plurality of RJ-45 network connectors for networkring connectivity of the bank and for access to the bank, for a locallyconnected terminal, such as a Universal Serial Bus (“USB”) and/or IEEE1394 connector, and a power connector 24 for powering the left mostmodule 12, and in turn, the bank of PLC modules 10. Any otheradvantageous connection may also be provided as understood in the art.

I/O modules 14, 16 and 18 may each comprise a plurality of electricalterminals or terminal blocks, or screw terminals) 26, 28 and 30,respectively, on each enclosure for receiving electrical conductorsexposed on the surface of the enclosure. The conductors may couple toone or more external field devices (not shown), such as sensors and/oractuators interacting with industrial controlled processes and/ormachines. Within each I/O module 14, 16 and 18, the electrical terminalsmay be routed to one or more internal bus slots, and in turn, toreleasably received function cards held within the one or more internalbus slots, or to equivalently embedded logic.

The electrical terminals 26, 28 and 30 on each of the I/O modules 14, 16and 18 may be divided into a first row of electrical terminals 32 forcommunicating with field devices, a second row of electrical terminals34 for providing a ground signal to the field devices and a third row ofelectrical terminals 36 for providing a power signal to the fielddevices. In a preferred embodiment, each of the electrical terminals inthe second row 34 of a particular I/O module may be coupled together,and each of the electrical terminals in the third row 36 of a particularI/O module may be coupled together. However, in an alternativeembodiment, some or all of the electrical terminals in the second row 34and/or some or all of the electrical terminals in the third row 36 maybe isolated from others to provide a plurality of power and/or groundsignals from the same I/O module, such as AC and DC power signals.

Power originating from a power source may be provided as alternatingcurrent (“AC”), such as in the range of 87 to 265 Volts at 50 to 60Hertz, and/or as direct current (“DC”), such as in the range of 18 to 32Volts. The left most module 12 may receive, for example, an AC powersignal from an AC power source (or a DC power signal from a DC powersource) via power connector 24. In a daisy chain topology, the left mostmodule 12 may then provide the power signal at electrical terminal 38,and a ground signal at electrical terminal 40, with the electricalterminals 38 and 40 each exposed on the surface of the enclosure of theleft most module 12. The power signal may be passed from the left mostmodule 12 to the neighboring I/O module 14 via a jumper connectionbetween the electrical terminal 38 on the left most module 12 and theelectrical terminal 39 on the I/O module 14, and the ground signal maybe passed via a jumper connection between the electrical terminal 40 onthe left most module 12 and the electrical terminal 41 on the I/O module14. The power signal may then be passed from the I/O module 14 to thenext neighboring I/O module 16 via a jumper connection between theelectrical terminal 42 on the I/O module 14 and the electrical terminal43 on the I/O module 16, and the ground signal may be passed via ajumper connection between the electrical terminal 44 on the I/O module14 and the electrical terminal 45 on the I/O module 16. The power signalmay then be passed from the I/O module 16 to the next neighboring I/Omodule 18 via a jumper connection between the electrical terminal 46 onthe I/O module 16 and the electrical terminal 47 on the I/O module 18,and the ground signal may be passed via a jumper connection between theelectrical terminal 48 on the I/O module 16 and the electrical terminal49 on the I/O module 18.

Each of the I/O modules 14, 16 and 18 may include, for example, one ormore light emitting diodes (“LED's”) 52, 53, 54, 55, 56 and 57reflecting the presence and/or nature of the power signal provided.Similarly, the left most module 12 may include, for example, LED's 50and 51. One LED may indicate the presence of an AC power signal, whereasanother LED may indicate the presence of a DC power signal.Alternatively, a single bi-colored LED may be used in which red or othercolor illumination indicates the presence of an AC power signal, and ayellow or different color illumination indicates the presence of a DCpower signal. Also, a lack of illumination may indicate a lack of anytype of power available. Various LED colors and affixed labeling mayalso be employed.

In an alternative embodiment, the left most module 12 may insteadprovide the power and ground signals in a daisy chain topology toneighboring I/O modules via side by side electrical connections asdescribed with respect to FIG. 2 below. In another alternativeembodiment, one or more of the I/O modules 14, 16 and 18 may receive,for example, a power signal from a power source via dedicated localpower connectors in a star topology, and may, in turn, provide the powerand ground signals at the electrical terminal exposed on the surface ofthe enclosure of the I/O modules as desired. Of course, any combinationof the above techniques may be employed as understood by one of ordinaryskill in the art.

Referring now to FIG. 2, an isometric view of the I/O module 14 isshown. I/O module 14 may comprise an enclosure providing a left flankingside 70 and a right flanking side 72. Each side may further comprise areleasable electrical connector 74 with a mechanical mechanism supportedon each flanking side exposed to connect adjacent modules on the leftand right sides. I/O module 14 may further comprise a releasablemechanical connector 76 for holding the I/O module 14 in proximity tothe modules on the left and right sides. The releasable mechanicalconnector may be adapted to hold the I/O module 14 by attachment to aDIN rail 78. The I/O module 14 may include internal bus slots 80 and 82for releasably receiving function cards.

Referring now to FIG. 3, an electronic circuit 100 that deciphersbetween AC and DC input signals in accordance with an embodiment of thepresent invention is shown. The circuit 100 may receive a positive DCinput signal 102 or an AC input signal 104, and a ground signal, forexample, at a pair of electrical terminals 106 and 108. The input signalmay then couple to a series inductor 110, which may be 10 mH, providingAC filtering and choke. The input signal may then be sent in twodirections, a first direction having a DC filter, herein comprising aseries diode 112, which may be rated to +600 Volts DC, and a seconddirection having an AC filter, herein comprising a series capacitor 114,which may be about 1 μF. The AC filter permits an AC signal to pass to afirst leg 116 of the circuit 100 and prevents a DC signal from passingto the first leg 116. The positive voltage with respect to ground in thefirst leg 116 during an AC positive excursion is the voltage of Zenerdiode 140, wherein the cathode of the Zener diode 140 is coupled to theAC filter and the anode of the Zener diode 140 is coupled to ground; theAC negative excursion is the forward voltage drop of the Zener diode140. The DC filter permits a DC signal to pass to the second leg 118 ofthe circuit 100, and allows only the positive AC signal to the secondleg 118, thereby preventing at least part of an AC signal from passingto the second leg 118.

If the input signal is the positive DC input signal 102, the signal(output of the DC filter) passes to the second leg 118 to produce anoutput for indicating a positive DC input signal. This may occur by thesignal (output of the DC filter) passing to a constant current source120 in series with an LED 122 coupled to ground. The constant currentsource 120 may comprise, for example, a larger resistor 124, which maybe about 2 MΩ, coupled between the gate and drain of an n-channel metaloxide semiconductor field effect transistor (“MOSFET”) 126, an NPNbipolar junction transistor (“BJT”) 128 with the base of the BJT 128coupled to the source of the MOSFET 126 and the collector of the BJT 128coupled to the gate of the MOSFET 126, and a smaller resistor 130, whichmay be about 100Ω, coupled between the base and the emitter of the BJT128. In operation, following the DC filter, the signal passes to thesecond leg 118, enters the constant current source 120 at the drain ofthe MOSFET 126, exits the constant current source 120 at the emitter ofthe BJT 128 (having a current strength of about 10 mA), and illuminatesthe LED 122.

If, on the other hand, the input signal is the AC input signal 104, thesignal (output of the AC filter) passes to the first leg 116 to producean output for indicating an AC input signal and causes a lock outcircuit to prevent the second leg 118 from producing the output forindicating a DC input signal. This may occur by the signal (output ofthe AC filter) in the first leg 116 being, rectified and passed in twodirections: (i) to a diode 146, then to a constant current source 148 inseries, then to an LED 150 in series coupled to ground, and (ii) tocircuitry in the first leg 116 used to control circuitry in the secondleg 118. The signal (output of the AC filter) may be rectified in thefirst leg 116 by a Zener diode 140 with the cathode of the Zener diode140 coupled to the signal (output of the AC filter) and the anode of theZener diode 140 coupled to ground, a diode 142 with the anode of thediode 142 coupled to the signal (output of the AC filter) and thecathode of the diode 142 coupled to a resistor 144 to ground, which maybe about 46.4 KΩ, and a capacitor 160, which may be about 2.2 μF,coupled between the cathode of the diode 142 and ground (in parallelwith the resistor 144).

As mentioned above, the signal (output of the AC filter), which has beenrectified, may be passed to the diode 146, then to the constant currentsource 148 in series, which may comprise, for example, a larger resistor152, which may be about 10 KΩ, coupled between the gate and drain of ann-channel MOSFET 154, an NPN BJT 156 with the base of the BJT 156coupled to the source of the MOSFET 154 and the collector of the BJT 156coupled to the gate of the MOSFET 154, and a smaller resistor 158, whichmay be about 49.9Ω, coupled between the base and the emitter of the BJT128, then to the LED 150 in series coupled to ground, in operation,following the diode 146, the signal passes to the constant currentsource 148 at the drain of the MOSFET 154, exits the constant currentsource 148 at the emitter of the BJT 156 (having a current strength ofabout 10 mA), and illuminates the LED 150.

Also as mentioned above, the signal (output of the AC filter), which hasbeen rectified, may be used (indirectly) to control circuitry in thesecond leg 118. For example, the cathode of the diode 142 may be coupledto the gate of an n-channel MOSFET 162. The source of the MOSFET 162 maybe coupled to ground, and the drain of the MOSFET 162 may be coupled tothe gate of the MOSFET 126 in the second leg 118. In operation,following rectification of the signal (output of the AC filter), thegate of the MOSFET 162 is held high, causing the MOSFET 162 to pull thegate of the MOSFET 126 low, which thereby inhibits current from flowingthrough the constant current source 120 to illuminate the LED 122.

In an alternative embodiment, the circuit 100 may be adapted to producean additional output for indicating a negative DC input signal, or maybe adapted to produce an output for indicating a negative DC inputsignal instead of a positive DC input signal. For example, in thecircuit 100, if an additional output for indicating a negative DC inputsignal is desired, the circuit components 112, 124, 126, 128, 130 and122 may be replicated as components 112′, 124′, 126′, 128′, 130′ and122′ in an additional leg in which the direction of the diode 112′ isreversed, the MOSFET 126′ is a p-channel MOSFET, the BJT 128′ is a PNPBJT and the direction of the LED 122′ is reversed. Similarly, if anoutput for indicating a negative DC input signal is desired instead ofan output for indicating a positive DC input signal, the circuitcomponents 112, 124, 126, 128, 130 and 122 may be replaced by thecomponents 112′, 124′, 126′, 128′, 130′ and 122′ in which the directionof the diode 112′ is reversed, the MOSFET 126′ is a p-channel MOSFET,the BJT 128′ is a PNP BJT and the direction of the LED 122′ is reversed.

Referring now to FIG. 4, another embodiment of an electronic circuit 200that deciphers between AC and DC input signals is shown. Similar to thecircuit 100 as described above with respect to FIG. 3, in the circuit200, if an input signal is a DC input signal 202, the signal passes to aconstant current source 220 in a second leg 218, and if the input signalis an AC input signal 204, the signal passes to a first leg 216 in whichit is rectified and passed in two directions: (i) to a diode 246, thento a constant current source 248 in series, and (ii) to circuitry in thefirst leg 216 used to control circuitry in the second leg 218. However,unlike the circuit 100 as described above, the constant current source220 in the second leg 218 and the constant current source 248 in thefirst leg 216 do not each couple to LED's. Instead, the constant currentsource 220 in the second leg 218 couples in series to the anode of adiode 222, and the constant current source 248 in the first leg 216couples in series to the anode of a diode 250. The cathode of the diode222 and the cathode of the diode 250 may couple together and, in turn,couple in series to the anode of LED 280. In operation, if the inputsignal is either the DC input signal 202 or the AC input signal 204, theLED 280 will illuminate. In an alternative embodiment, the diodes 222and 250 may be replaced with LED's, providing an electronic circuit thatdeciphers between AC and DC input signals with three LED's.

As described above with respect to FIG. 1, Various LED colors andaffixed labeling may also be employed. In addition, alternativeembodiments may provide other output mechanisms for signaling between ACand DC input signals. For example, instead of or in addition to LED's, aspeaker may be configured in each leg, including with push buttonactivation or silencing, to produce variable audible tones todistinguish between AC and DC input signals present. Also, instead of orin addition to LED's, the output of each, leg may be digitized andcoupled as binary bits to a logic controller to flag the presence of ACor DC input signals. Indeed, a variety of other alert mechanisms may beemployed as understood by one of ordinary skill in the art.

Referring now to FIG. 5, a diagram showing an industrial controller I/Omodule 300 and a field device 400, each in accordance with an embodimentof the present invention, is shown. The I/O module 300 may comprise aleft electrical connector 302 and a right electrical connector 304 onflanking sides exposed to connect to adjacent modules on the left andright sides (not shown). The electrical connector 302 and 304 mayprovide a common system backplane, including communications, power andground signals as described. A first communications signal 306 maycouple between the left electrical connector 302 and a logic controller316 in the I/O module 300, and a second communications signal 307 maycouple between the logic controller 316 and the right electricalconnector 304 to form a network ring with the adjacent modules on theleft and right sides. The logic controller 316 may comprise, forexample, a function card releasably received in an internal bus slotand/or embedded logic. A module power signal 308, which may be a DCpower signal from the adjacent module on the left side, may couplebetween the left electrical connector 302 and the right electricalconnector 304 and may provide power to the I/O module 300 as necessary,including to the logic controller 316.

The logic controller 316 may couple to a plurality of electricalterminals (or terminal blocks, or screw terminals) 318 on the surface ofthe enclosure of the I/O module 300. The electrical terminals 318 mayreceive electrical conductors which may couple to one or more externalfield devices. The electrical terminals 318 are divided into a first rowfor communicating with field devices, a second row for providing aground signal to the field devices and a third row for providing a powersignal to the field devices. In this embodiment, each of the electricalterminals 318 in the second row are coupled together, providing a commonground signal, and each of the electrical terminals 318 in the third roware, coupled together, providing a common power signal. Here, electricalterminal 320 in the first row communicates with a field logic controller402 in a field device 400 via conductor 322, electrical terminal 324 inthe second row provides a ground signal to the field device 400 viaconductor 326, and electrical terminal 328 in the third row provides apower signal to the field device 400 via conductor 330.

In one embodiment, an electrical terminal in the second row of the I/Omodule may receive a power and/or ground signal from one neighboring I/Omodule via a jumper connection, and another electrical terminal of, theI/O module may provide the power and/or ground signal to anotherneighboring I/O module via another jumper connection. For example, I/Omodule 300 may receive a ground signal at electrical terminal 332 in thesecond row from the adjacent module on the left side and may provide theground signal at electrical terminal 334 in the second row to theadjacent module on the right side, and I/O module 300 may receive apower signal at electrical terminal 336 in the third row from theadjacent module on the left side and may provide the power signal atelectrical terminal 338 in the third row to the adjacent module on theright side.

In another embodiment, the I/O module 300 may instead receive andprovide power and/or ground signals via the electrical connections sideby side. For example, a DC power signal 309 and ground signal 310provided from the adjacent module on the left side may couple betweenthe left electrical connector 302 and the right electrical connector 304and may couple to power logic 340. An AC power signal 312 and groundsignal 314 also provided from the adjacent module on the left side mayalso couple between the left electrical connector 302 and the rightelectrical connector 304 and may also couple to the power logic 340. Thepower logic 340, which may be controlled by the logic controller 316,may select which power and/or ground signals to couple to whichelectrical terminals as desired. For example, the power logic 340 mayprovide the DC power signal 309 to electrical terminal 338 in the thirdrow via connection 342, and the power logic 340 may provide the groundsignal 310 to electrical terminal 334 in the second row via connection344.

In yet another alternative embodiment, the I/O module 300 may receive,for example, power and/or ground signals from a power source viaconnection 346, and may provide the power and/or ground signals to theelectrical terminals as desired. Of course, any combination of the abovetechniques may be employed as understood by one of ordinary skill in theart. As such, the I/O module 300 may provide a detection and/orindication of the nature of power being provided, and/or the fielddevice may provide a detection and/or indication of the nature of powerbeing received.

Here, the I/O module 300 includes an electronic circuit 350 thatdeciphers between AC and DC input signals in accordance with anembodiment of the present invention. The circuit 350 may receive a powersignal from electrical terminal 336 in the third row via connection 352,and may receive a ground signal from electrical terminal 332 in thesecond row via connection 354. In response, the circuit 350 mayilluminate LED 356 for indicating a DC power signal via connection 358,or may illuminate LED 360 for indicating an AC power signal viaconnection 362. The I/O module 300 may also include detection logic 364coupled between the circuit 350 and the logic controller 316 which may,for example, provide a digitized output to the logic controller 316 toflag the presence of AC or DC input signals, or may adjust one or moreother properties of the circuit 350.

Similarly, the field device 400 includes an electronic circuit 410 thatdeciphers between AC and DC input signals in accordance with anembodiment of the present invention. The circuit 410 may receive a powersignal from electrical terminal 328 in the third row via conductor 330,and may receive a ground signal from electrical terminal 324 in thesecond row via conductor 326. In response, the circuit 410 mayilluminate LED 412 for indicating a DC power signal via connection 414,or may illuminate LED 416 for indicating an AC power signal viaconnection 418. The field device 400 may also include field power logic420 which may, upon the circuit 410 indicating safe power to the fieldpower logic 420 via connections 414 and 418, safely provide power to thefield logic controller 402 and the field device 400 as necessary. Thefield device 400 may also include field detection logic 422 coupledbetween the circuit 410 and the field logic controller 402, and/orcoupled between the circuit 410 and the field power logic 420, whichmay, for example, provide a digitized output to the field logiccontroller 402 and/or the field power logic 420 to flag the presence ofAC or DC input signals, or may adjust one or more other properties ofthe circuit 410.

Referring now to FIG. 6, an isometric view of a handheld diagnosticprobe 460 in accordance with an embodiment of the present invention isshown. The probe 460 includes an electronic circuit that deciphersbetween AC and DC input signals in accordance with an embodiment of thepresent invention. Such a probe may be used, for example, by atechnician to safely determine the presence of AC and DC input signalswhile reducing the risk of catastrophic results. A tip 462 on the probe460 may touch, for example, an electrical terminal exposed on thesurface of an I/O module. Accordingly, the tip 462 may input theresulting signal to the circuit. In response, the circuit may illuminateLED 464 for indicating a DC power signal, or may illuminate LED 466,and/or may illuminate LED 468 for indicating a DC or AC power signal.The probe 460 may also include a speaker 470, which may produce variableaudible tones to distinguish between AC and DC input signals present,and a push button 472 which may silence such tones. The probe 460 mayalso include cabling 474 for providing power, ground and datacommunications, including providing a digitized output to a remotedevice for indicating the presence of an AC or DC input signal, thoughin an alternative embodiment the probe 460 may include such featureswirelessly.

Referring now to FIG. 7, a flog diagram illustrating a method fordeciphering between an AC and a DC input signal in accordance with anembodiment of the present invention. In step 500, an input signal isreceived. Next, in step 502, an AC component of the input signal ispermitted to pass to a first leg of a circuit while a DC component ofthe input signal is prevented from passing to the first leg. Next, instep 504, a DC component of the input signal is permitted to pass to thesecond leg of the circuit while an AC component of the signal isprevented from passing to the second leg. Next, in decision step 506, itis determined if an AC component of the input signal passed to the firstleg. If an AC component of the input signal passed to the first leg,then, in step 508, a first output for indicating an AC input signal isproduced, then, in step 510, the second leg is prevented from producinga second output. However, as determined in decision step 506, if an ACcomponent of the input signal did not pass to the first leg, then, indecision step 512, it is determined if a DC component of the inputsignal passed to the second leg. If a DC component of the input signalpassed to the second leg, then, in step 514, a second output forindicating a DC input signal is produced. After the second leg isprevented from producing a second output in step 510, or after thesecond output for indicating a DC input signal is produced in step 514,the method may repeat from step 500.

Certain terminology is used herein for purposes of reference only, andthus is not intended to be limiting. For example, terms such as “upper,”“lower,” “above,” and “below” refer to directions in the drawings towhich reference is made. Terms such as “front,” “back.” “rear,”“bottom,” “side,” “left” and “right” describe the orientation ofportions of the component within a consistent but arbitrary frame ofreference which is made clear by reference to the text and theassociated drawings describing the component under discussion. Suchterminology may include the words specifically mentioned above,derivatives thereof, and words of similar import. Similarly, the terms“first,” “second” and other such numerical terms referring to structuresdo not imply a sequence or order unless clearly indicated by thecontext.

When introducing elements or features of the present disclosure and theexemplary embodiments, the articles “a,” “an,” “the” and “said” areintended to mean that there are one or more of such elements orfeatures. The terms “comprising,” “including” and “having” are intendedto be inclusive and mean that there may be additional elements orfeatures other than those specifically noted. It is further to beunderstood that the method steps, processes, and operations describedherein are not to be construed as necessarily requiring theirperformance in the particular order discussed or illustrated, unlessspecifically identified as an order of performance. It is also to beunderstood that additional or alternative steps may be employed.

References to “a microprocessor” and “a processor” or “themicroprocessor” and “the processor” can be understood to include one ormore microprocessors that can communicate in a stand-alone and/or adistributed environment(s), and can thus be configured to communicatevia wired or wireless communications with other processors, where suchone or more processor can be configured to operate on one or moreprocessor-controlled devices that can be similar or different devices.Furthermore, references to memory, unless otherwise specified, caninclude one or more processor-readable and accessible memory elementsand/or components that can be internal to the processor-controlleddevice, external to the processor-controlled device, and can be accessedvia a wired or wireless network.

It is specifically intended that the present invention not be limited tothe embodiments and illustrations contained herein and the claims shouldbe understood to include modified forms of those embodiments includingportions of the embodiments and combinations of elements of differentembodiments as coming within the scope of the following claims. All ofthe publications described herein including patents and non-patentpublications are hereby incorporated herein by reference in theirentireties.

The present invention may be part of a “safety system” used to protecthuman life and limb in a field, warehouse, factory or industrialenvironment. Nevertheless, the term “safety,” “safely” or “safe” as usedherein is not a representation that the present invention will make theenvironment safe or that other systems will produce unsafe operation.Safety in an industrial process depends on a wide variety of factorsoutside of the scope of the present invention including: design of thesafety system, installation and maintenance of the components of thesafety system, and the cooperation and training of individuals using thesafety system. Although the present invention is intended to be highlyreliable, all physical systems are susceptible to failure and provisionmust be made for such failure.

What is claimed is:
 1. An electronic circuit for deciphering between anAC and a DC input signal comprising: an AC filter receiving an inputsignal and coupled to a first leg, the AC filter permitting an AC signalto pass to the first leg and preventing a DC signal from passing to thefirst leg; and a DC filter receiving the input signal and coupled to asecond leg, the DC filter permitting a DC signal to pass to the secondleg and preventing at least part of an AC signal from passing to thesecond leg; wherein a DC signal passing to the second leg causes thesecond leg to produce a second output for indicating a DC input signal,and an AC signal passing to the first leg causes the first leg toproduce a first output for indicating an AC input signal and causes alock out circuit to prevent the second leg from producing the secondoutput.
 2. The electronic circuit of claim 1, wherein the AC filtercomprises a series capacitor.
 3. The electronic circuit of claim 1,wherein the DC filter comprises a series diode.
 4. The electroniccircuit of claim 1, further comprising the first and second outputscoupled together to produce a third output for indicating an AC or a DCinput signal.
 5. The electronic circuit of claim 1, wherein the firstand second outputs are coupled to light emitting diodes.
 6. Theelectronic circuit of claim 1, wherein the first and second outputsproduce audible tones.
 7. The electronic circuit of claim 1, wherein thefirst and second outputs produce digital data signals.
 8. The electroniccircuit of claim 1, wherein the lock out circuit comprises a transistorin the second leg controlled by circuitry in the first leg.
 9. Aprogrammable logic controller module for providing power to a fielddevice comprising: an enclosure; an electrical terminal on the enclosurecoupled to a power signal; an AC filter contained in the enclosurereceiving the power signal and coupled to a first Leg of a circuit, theAC filter permitting an AC signal to pass to the first leg andpreventing a DC signal from passing to the first leg; and a DC filtercontained in the enclosure receiving the power signal and coupled to asecond leg of the circuit, the DC filter permitting a DC signal to passto the second leg and preventing at least part of an AC signal frompassing to the second leg; wherein a DC signal passing to the second legcauses the second leg to produce a second output for indicating a DCpower signal, and an AC signal passing to the first leg causes the firstleg to produce a first output for indicating an AC power signal andcauses a lock out circuit to prevent the second leg from producing thesecond output.
 10. The programmable logic controller module of claim 9,wherein the AC filter comprises a series capacitor.
 11. The programmablelogic controller module of claim 9, wherein the DC filter comprises aseries diode.
 12. The programmable logic controller module of claim 9,further comprising the first and second outputs coupled together toproduce a third output for indicating an AC or a DC input signal. 13.The programmable logic controller module of claim 9, wherein the firstand second outputs are coupled to light emitting diodes.
 14. Theprogrammable logic controller module of claim 9, wherein the first andsecond outputs produce audible tones.
 15. The programmable logiccontroller module of claim 9, wherein the first and second outputsproduce digital data signals.
 16. The programmable logic controllermodule of claim 9, wherein the lock out circuit comprises a transistorin the second leg controlled by circuitry in the first leg.
 17. A methodfor deciphering between an AC and a DC input signal comprising: (a)receiving an input signal; (b) permitting an AC component of the inputsignal to pass to a first leg of a circuit while preventing a DCcomponent of the input signal from passing to the first leg; (c)permitting a DC component of the input signal to pass to a second leg ofthe circuit while preventing at least part of an AC component of thesignal from passing to the second, leg; and (d) producing a secondoutput for indicating a DC input signal following a DC component of theinput signal passing to the second leg, and producing a first output forindicating an AC input signal and preventing the second leg fromproducing the second output following an AC component of the inputsignal passing to the first leg.
 18. The method of claim 17, whereinproducing an output illuminates a light emitting diode.
 19. The methodof claim 17, wherein producing an output produces an audible tone. 20.The method of claim 17, wherein producing an output produces a digitaldata signal.